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Wireless Mesh Networks (WMN)
Mesh is a technology that comes from the optical networking world and has been adapted to the Ethernet market. Mesh is a very smart way to provide resilient networks. Mesh architecture creates the opportunity to change data paths within a second when problems occur. Compared to the older solutions for network resilience, mesh really was a big step forward.
In the Ethernet WAN world mesh has been fully implemented and widely accepted. In the smaller Ethernet LAN world however nobody is using it. The question can be asked, why is everybody discussing (needing) this in the WLAN Ethernet world?
Obviously mesh is mainly related to city-wide (outdoor) Wireless LAN networks and those indoor networks where there are no Ethernet cables available. This immediately explains why mesh has become so popular. Particularly in these networks the radios have to rely on each other to build a successful WAN access, and when one radio fails another has to maintain the path to the WAN. Also the mesh standard is built in such a way that radios are able to find each other easily without any human interference: mesh has its own intelligence!
So, why isn’t everybody using mesh today as its advantages seem to be so appealing? The main reasons why we don’t advise the use of mesh are the negative sides of mesh: bandwidth consumption and lack of interoperability.
Bandwidth (double use):
WLAN has already the disadvantage that almost 50% of the gross data rate has to be used for overhead. These overheads are really important to get stable links and to transmit the data without interruption. To build a mesh network another 50% of the available data-rate has to be reserved for the fault-back path. As such, radios are sending the same data twice. With the continued rapid growth of bandwidth demand, WMN are unlikely to be able to deliver the speeds required by consumers.
The IEEE has ratified the 802.11s standard to make a first step into the mesh world. The standard explains how multivendor networks can be built by setting up alternative paths based on Layer 2. It sadly missed the needed mesh-intelligent (layer 3) level, so every mesh vendor is still offering his own proprietary solution.
Still we think that mesh is a very good standard and to be used where it can be used, but as LAN isn’t using it today, why should WLAN do it? There isn’t enough bandwidth available to deliver effective WLAN mesh networks. This may be solved when 802.11ac or 802.11ad become effective, however until that time we don’t advise the use of Wireless Mesh.
WLAN Consulting is an initiative of LANCOM Systems. LANCOM Systems is a leading German manufacturer of wireless LAN technology based on industry standards.